It’s only been in the past few years that scientists have worked out how certain genes influence the color of mammals. Pigment-producing cells called melanocytes can generate a range of hues, depending on the signals they receive. When certain proteins latch onto a receptor on melanocytes, for example, the cells produce dark pigments. If they don’t latch onto the receptor, called Mc1r, the cells make yellow or reddish pigments. Mutations to Mc1r can influence how strongly they relay their signals, and thus change the colors the cells produce. In humans, for example, variants of Mc1r produce red hair.

Dawn Marshall, a biologist at Memorial University of Newfoundland, and her colleagues, recently studied three white coyotes, sequencing their genes for Mc1r, along with two other genes known to be involved in color. They compared genes of the white coyotes to those of 59 ordinary coyotes to see if they could find any differences. And they did. They found that white coyotes carried two copies of the same variant of Mc1r. Some dark coyotes had the same variant, but only carried one copy; their other copy was a normal version. In other words, it appears that the white Mc1r gene is recessive. It takes two copies to turn a coyote white.

What makes that discovery particularly intriguing is that other scientists have seen the same mutation in Mc1r before: in golden retrievers. In the dogs, it appears to blunt the dark-pigment signals, causing them to grow light hairs.

These two findings may be no coincidence. During the coyote breeding season on Newfoundland in March 2001, a male Golden Retriever ran off with a coyote and was never seen again. It’s possible that the dog and the coyote interbred, and some of their coyote-dog hybrid pups inherited the Mc1r mutation. The coyotes that carried a single copy of the Golden Retriever gene would have looked ordinary. But from time to time, two coyotes with the gene would mate. And when a coyote pup inherited two copies of the mutant Mc1r gene, its coat became lighter. But in a coyote, these genes didn’t turn fur gold. They transformed the coyotes into snow."